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FreeBSD-SA-11:05.unix                                       Security Advisory
                                                          The FreeBSD Project

Topic:          Buffer overflow in handling of UNIX socket addresses

Category:       core
Module:         kern
Announced:      2011-09-28
Credits:        Mateusz Guzik
Affects:        All supported versions of FreeBSD.
Corrected:      2011-10-04 19:07:38 UTC (RELENG_7, 7.4-STABLE)
                2011-10-04 19:07:38 UTC (RELENG_7_4, 7.4-RELEASE-p4)
                2011-10-04 19:07:38 UTC (RELENG_7_3, 7.3-RELEASE-p8)
                2011-10-04 19:07:38 UTC (RELENG_8, 8.2-STABLE)
                2011-10-04 19:07:38 UTC (RELENG_8_2, 8.2-RELEASE-p4)
                2011-10-04 19:07:38 UTC (RELENG_8_1, 8.1-RELEASE-p6)
                2011-10-04 19:07:38 UTC (RELENG_9, 9.0-RC1)

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

0.   Revision History

v1.0  2011-09-28 Initial release.
v1.1  2011-10-04 Updated patch to add linux emulation bug fix.

I.   Background

UNIX-domain sockets, also known as "local" sockets, are a mechanism for
interprocess communication.  They are similar to Internet sockets (and
utilize the same system calls) but instead of relying on IP addresses
and port numbers, UNIX-domain sockets have addresses in the local file
system address space.

FreeBSD contains "linux emulation" support via system call translation
in order to make it possible to use certain linux applications without
recompilation.

II.  Problem Description

When a UNIX-domain socket is attached to a location using the bind(2)
system call, the length of the provided path is not validated.  Later,
when this address was returned via other system calls, it is copied into
a fixed-length buffer.

Linux uses a larger socket address structure for UNIX-domain sockets
than FreeBSD, and the FreeBSD's linux emulation code did not translate
UNIX-domain socket addresses into the correct size of structure.

III. Impact

A local user can cause the FreeBSD kernel to panic.  It may also be
possible to execute code with elevated privileges ("gain root"), escape
from a jail, or to bypass security mechanisms in other ways.

The patch provided with the initial version of this advisory exposed
the pre-existing bug in FreeBSD's linux emulation code, resulting in
attempts to use UNIX sockets from linux applications failing.  The most
common instance where UNIX sockets were used by linux applications is
in the context of the X windowing system, including the widely used
linux "flash" web browser plugin.

IV.  Workaround

No workaround is available, but systems without untrusted local users
are not vulnerable.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 7-STABLE or 8-STABLE, or to
the RELENG_8_2, RELENG_8_1, RELENG_7_4, or RELENG_7_3 security
branch dated after the correction date.

2) To update your vulnerable system via a source code patch:

The following patch has been verified to apply to FreeBSD 7.4, 7.3,
8.2 and 8.1 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch http://security.FreeBSD.org/patches/SA-11:05/unix2.patch
# fetch http://security.FreeBSD.org/patches/SA-11:05/unix2.patch.asc

NOTE: The patch distributed at the time of the original advisory fixed
the security vulnerability but exposed the pre-existing bug in the linux
emulation subsystem.  Systems to which the original patch was applied
should be patched with the following corrective patch, which contains
only the additional changes required to fix the newly-exposed linux
emulation bug:

# fetch http://security.FreeBSD.org/patches/SA-11:05/unix-linux.patch
# fetch http://security.FreeBSD.org/patches/SA-11:05/unix-linux.patch.asc

b) Apply the patch.

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

3) To update your vulnerable system via a binary patch:

Systems running 7.4-RELEASE, 7.3-RELEASE, 8.2-RELEASE, or 8.1-RELEASE on
the i386 or amd64 platforms can be updated via the freebsd-update(8)
utility:

# freebsd-update fetch
# freebsd-update install

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_7
  src/sys/kern/uipc_usrreq.c                                   1.206.2.13
  src/sys/compat/linux/linux_socket.c                           1.74.2.15
RELENG_7_4
  src/UPDATING                                             1.507.2.36.2.5
  src/sys/conf/newvers.sh                                   1.72.2.18.2.8
  src/sys/kern/uipc_usrreq.c                               1.206.2.11.4.2
  src/sys/compat/linux/linux_socket.c                       1.74.2.13.2.2
RELENG_7_3
  src/UPDATING                                             1.507.2.34.2.9
  src/sys/conf/newvers.sh                                  1.72.2.16.2.11
  src/sys/kern/uipc_usrreq.c                               1.206.2.11.2.2
  src/sys/compat/linux/linux_socket.c                       1.74.2.12.2.2
RELENG_8
  src/sys/kern/uipc_usrreq.c                                    1.233.2.6
  src/sys/compat/linux/linux_socket.c                           1.101.2.5
RELENG_8_2
  src/UPDATING                                             1.632.2.19.2.5
  src/sys/conf/newvers.sh                                   1.83.2.12.2.8
  src/sys/kern/uipc_usrreq.c                                1.233.2.2.2.2
  src/sys/compat/linux/linux_socket.c                       1.101.2.3.4.2
RELENG_8_1
  src/UPDATING                                             1.632.2.14.2.8
  src/sys/conf/newvers.sh                                   1.83.2.10.2.9
  src/sys/kern/uipc_usrreq.c                                1.233.2.1.4.2
  src/sys/compat/linux/linux_socket.c                       1.101.2.3.2.2
RELENG_9
  src/sys/kern/uipc_usrreq.c                                    1.244.2.2
  src/sys/compat/linux/linux_socket.c                           1.108.2.2
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/7/                                                         r226023
releng/7.4/                                                       r226023
releng/7.3/                                                       r226023
stable/8/                                                         r226023
releng/8.2/                                                       r226023
releng/8.1/                                                       r226023
stable/9/                                                         r226023
- -------------------------------------------------------------------------

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-11:05.unix.asc
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